1. Field of Invention
This invention relates to systems and methods that standardize reproducible illumination within an instrument line. In particular, the invention is directed to an illumination system that preferably uses solid-state devices regulated by a control system to illuminate sample parts. The illumination system is calibrated with a reference illumination source to provide stable, compensated standardized systems and methods that measure the intensity of light used to illuminate a sample part.
2. Description of Related Art
Current commercial metrology systems based on video inspection almost exclusively use tungsten filament lamps, e.g., halogen lamps, when performing measurements transmission, direct reflection or diffuse illumination modes. Halogen lamps are typically used because they have a reliable lifetime of approximately 2000 hours. These lamps also have sufficient energy in the visible portion of the spectrum and are relatively inexpensive. These lamps have characteristics similar to blackbodies near 2700 K-3200 K.
As a result of the broadband emission characteristics of halogen lamps, a majority of the commercial vision measurement system manufacturers spectrally limit the radiation emitted from the halogen lamps to exclude, for example, radiation in the wavelength range from 750 nm to 3.5 .mu.m. This can raise the signal to noise ratio (SNR) for measurements performed in the visible region and permits a reduction in the sophistication required of the imaging optics. The spectral limitation also excludes a radiometrically sensitive region for silicon from being exploited for vision measurements.
However, incorporating hardware to operate halogen-lamp-based illumination systems is bulky, expensive and relatively unreliable compared to illumination systems using solid-state sources. Conventional vision systems have minimum requirements for spectrally unfiltered optical power on the order of 25 watts for illumination sources. Driving such illumination systems translates to source currents in the range of, for example, 0.6-2.0 amperes. Other vision systems can have even higher current drive requirements.
Typically, conventional illumination sources are remotely located because a significant amount of heat is generated by the illumination sources. If the heat generated by the illumination system is not accounted for, the accuracy of dimensional measurements in vision instruments could be compromised. The illumination sources are therefore spectrally low-pass filtered at, for example, a wavelength of about 750 nm.
Hence, an apparatus is needed to transport the light from the remote location of the illumination source to the point of use or measurement. Typically, this is accomplished using multimode glass fiber bundles. However, even low quality illumination bundles are known to be expensive, fragile and often not necessary for most users from a convenience standpoint.